(1) Field of the Invention
This invention relates to edge exposing apparatus for emitting light to and exposing edge regions of substrates such as semiconductor wafers, glass substrates for liquid crystal displays, glass substrates for photomasks, or substrates for optical disks (hereinafter called simply substrates).
(2) Description of the Related Art
In a conventional edge exposing apparatus, a light guide in the form of a bundle of optical fibers guides light emitted from a light source unit (light emitting unit) to irradiate and expose edge regions of each substrate. Such an apparatus has only one light source unit, and cannot perform an edge exposing operation in time of changing a lamp in the light source. Japanese Unexamined Patent Publication No. 2002-313708 discloses an apparatus for solving this problem to improve throughput of the edge exposing operation. The apparatus disclosed therein exposes substrate edges by mixing lights emitted from a plurality of light source units. This apparatus, while a lamp in one light source unit is changed, can continue an edge exposing operation using the remaining light source unit(s).
However, the conventional apparatus noted above has the following problems (I) and (II):
Problem (I)
It is difficult to assess a lowering of performance of a light source unit, which points to a necessity to change the lamp. In practice, the lamp is changed only after the performance of the light source unit lowers to the extent of causing trouble in edge exposure. Consequently, while the necessity is felt for a change, the other light source unit also may lower in performance so that the apparatus is unable to effect edge exposure. In addition, it takes time (e.g. about seven minutes) after the light source unit with a new lamp emits light (i.e. after startup of the light source unit) and before the light source unit is in a ready state for performing edge exposure (e.g. before stabilization of the light from the light source unit). When, after changing the lamp, edge exposure is performed using the new, changed light source unit, light may be emitted in an unstable state, resulting in a reduced quality of substrates.
Problem (II)
As described above, the light emitted from a light emitting unit is guided by a light guide in the form of a bundle of optical fibers to irradiate edge regions of a substrate. The light guided by the optical fibers has a non-uniform intensity distribution due to the fibers.
To eliminate this non-uniformity, the apparatus disclosed in Japanese Unexamined Patent Publication No. 2002-313708 noted above has a light guide divided into a first light guide and a second light guide, with a light mixing optical element interposed between the first light guide and second light guide. The light emitted from the light emitting unit is guided by the first light guide, and components of the light in the strands of the respective fibers forming the first light guide are mixed by the light mixing optical element. The mixed light is guided by the second light guide to exit to the edge regions of the substrate. This makes the non-uniform luminous intensity distribution into a uniform distribution. Where a plurality of light emitting units are provided, the light emitted from each light emitting unit is guided by the first light guide, and mixed by the light mixing optical element. The mixed light is guided by the second light guide to exit to the edge regions of the substrate to effect edge exposure.
However, the light guided by and exiting the second light guide has a rugged profile reflecting the configuration of the strands of the optical fibers (i.e. cross sections of the fibers) forming the second light guide. The profile of the light may be adjusted by arranging strip-shaped slits at a rugged boundary through which the light is emitted. Then, it is time-consuming and troublesome to put the strands of the fibers in order and arrange the slits.